The present invention concerns stabilization of polyoxyalkylene polyether polyols and the use of the stabilized polyols in the preparation of polyurethane foam. In particular the invention relates to stabilization of polyols with certain liquid stabilizer compositions and the color or scorch inhibition of flexible and semiflexible polyurethane foams made from the stabilized polyols.
Prior art methods for stabilization of polyoxyalkylene polyether polyols with antioxidants or stabilizers and the use of the stabilized polyols in the preparation of polyurethane foams to inhibit scorch are well known.
U.S. Pat. No. 3,567,664 and U.S. Pat. No. 3,637,865 disclose polyurethane foams stabilized with a mixture of butylated hydroxytoluene (BHT) and p,p'-dialkyldiphenylamine. U.S. Pat. No. 4,010,211 teaches the addition of phenothiazine to the BHT/p,p'-dialkyldiphenylamine mixture. U.S. Pat. No. 4,794,126 discloses flame retardant polyurethane foams stabilized with a stabilizer package of diarylarylenediamine reaction product of diarylamine and alkyl ketone and a hindered phenol, in particular 3,6'-di-tert-butyl-4-sec-butylphenol. Statton, Evaluation of Hindered Phenols for Minimization of Foam Discoloration Using the Microwave Scorch Test, 20 J. CELLULAR PLASTICS 346 (1984) studied four phenols in combination with the solid antioxidant p,p'-dioctyldiphenylamine alone and in the presence of phenothiazine. Although systems with BHT were fairly effective, systems of 2,6-di-tert-butyl-4-sec-butylphenol and p,p'-dioctyldiphenylamine did not provide satisfactory scorch resistance.
Surprisingly, it has been discovered that good scorch resistance is imparted to polyurethane foams by utilizing novel liquid stabilizer compositions. The liquid compositions not only provide good color and scorch control for polyurethane foams, but also eliminate certain processing disadvantages associated with presently utilized solid stabilizer systems.
Conventional solid stabilizers are generally dissolved in the polyol media by heating. To remove any undissolved stabilizer solids, the entire voluminous polyol mass is subjected to a filtration step. Only then the polyol precursor can be cured to the final foam product.
Advantageously, the present liquid stabilizer compositions are readily soluble in the polyol media at ambient temperatures. Consequently, two steps of the conventional process may be eliminated: dissolution of the stabilizer in the polyol media by heating and removal of undissolved stabilizer solids by filtration. Furthermore, the liquid stabilizer compositions may be added to the polyol by metering or pumping for convenience and safety.